This invention is in the field of digital image processing, and is more specifically directed to the segmentation of a digital image to distinguish foreground and background subjects.
Digital cameras have now become commonplace in modern society, especially with the implementation of digital cameras in cellular telephone handsets. As is fundamental in the art, the digitization of a captured photographic image allows the image to be analyzed and processed by digital image processing techniques. Conventional digital image processing algorithms range from basic image “improvement” processing to optimize exposure, color saturation, and sharpness in the image, to the wholesale alteration of image subjects and of the image itself.
In digital image processing, the operation of segmentation refers to the analysis of a digital image to identify features or subjects in the image, and to extract those features or subjects from the image. In a general sense, segmentation partitions the digital image into a set of segments, where the pixels within a given segment have some similarity to one another in color, intensity, texture, etc., at least in a relative sense as compared with pixels in adjacent segments. Conventional image processing techniques used for segmentation of a digital image include “clustering” by way of an iterative statistical algorithm, analysis of the image based on a histogram of color or intensity (i.e., identifying pixels in a peak or valley of the histogram), edge detection algorithms, and similarity determination relative to neighboring pixels according to “region growing” methods, among others. Some segmentation algorithms are quite complicated, for example involving the analysis of two- or three-dimensional entropy functions.
Three-dimensional effects in still and video image display are again gaining popularity. Modem techniques for displaying a “3D” image or sequence of images on a conventional “2D” video display all require distinguishing features or subjects of the image that are near to the camera or viewer, from those that are farther away. Differences in perspective, color, polarization, or phase (i.e., for interference filter technology) are applied differently to the near and far subjects, which are discernible by the viewer either directly, or by wearing special glasses. As such, the segmentation of a two-dimensional digital image is useful in identifying and extracting features or subjects of the image based on their distance from the camera.